The present invention relates to a binding rubber extruder for retreading tires having an extruder head, an axis of which extends essentially vertically to a surface of a carcass, whereby the carcass is supported in a rotatably drivable manner and whereby a revolving speed of the carcass and an extrusion speed are adjusted relative to one another.
With a binding rubber extruder of the aforementioned kind that is used for retreading tires, a binding rubber Layer is applied to the roughened carcass before the application of the tread strip. Besides these binding rubber extruders which are also called CTC-extruders (cushion to casing), so called CTT-extruders (cushion to tread) are also known with which the binding rubber layer is applied to the tread strip. Both binding rubber extruders have advantages and disadvantages.
With the known CTC-extruder a careful application of the binding rubber is necessary which requires skilled personnel. The binding rubber strip is supplied in a coil with plastic layers positioned between the binding rubber strips. The intermediate plastic layer is removed and the binding rubber layer is applied to the carcass. Air inclusions and any kind of contamination must be avoided at all costs in order to not reduce the long-term quality of the retreading.
This manual application process results in good quality retreaded tires when the necessary care is provided but it is at the same time rather time consuming and labor intensive.
In another CTC-process narrow binding rubber strips are employed which are applied to the carcass by a machine, whereby the edges of the strips overlap to a certain extent or abut one another in order to cover the entire width of the carcass after a certain number of revolutions.
However, with this process it is difficult to avoid air inclusions on the one hand and to control the final thickness of the binding rubber Layer on the other hand. In a further process of the aforementioned kind it is suggested to directly apply the binding rubber layer to the carcass via an extruder head. The extruder head is of a special shape whereby the axis essentially extends vertically to the surface of the carcass. With this known process there is no nozzle employed but a Lip is provided which more or less exactly fits the contour of the carcass and extends downstream of the binding rubber outlet.
The lower lip is missing, and by exactly controlling the revolving speed of the carcass and the extrusion speed the binding rubber layer is applied to the carcass.
With this process small irregularities of the carcass are supposedly compensated since they are automatically filled. Due to the common binding rubber layer of a thickness of 1.5 mm this is however not achievable in practice.
With this method the carcass must be inflated to a high pressure thereby practically replacing the missing part of the nozzle. Since a certain untrue rotation of the carcass is however unavoidable, this method of applying the binding rubber layer results in a non-uniform thickness of the binding rubber layer on the carcass.
It is also disadvantageous that the profiled lip of the extruder head must be exchanged wit every change of tire type and size, in order to provide for the necessary adjustment.
It is therefore an object of the present invention to provide a binding rubber extruder with which the application of a binding rubber layer onto carcasses of different size and kinds is possible without having air inclusions, whereby, at the same time, the binding rubber layer is applied to untrue carcasses in a more uniform manner.